During the pioneering period of the birth and development of photography we know how many different processes of image reproduction were perfected and how the contact print was, for a long time, the only form of reproduction of the “photographs “; one of the processes that has come up to us nowadays in full health, even with some substantial changes from the original, is the cyanotype that is still practiced today thanks, probably, also to the extreme simplicity of its implementation.
The Cyanotype print process is the result of the insights of Sir John Herschel, a versatile British scientist who in the period from 1840 to 1842 developed this new technique, similar in many respects to the photogenic drawings made by Henry Fox Talbot, based on the sensitivity of salts of iron (instead of silver) to the effects of light; Herschel set up a process capable of exploiting the ability of light to transform trivalent iron salt into bivalent form, which by virtue of this transformation assumes a bluish-brown coloration.
By adhering the sensitive solution of trivalent salt to a support able to restrain it and interposing between this and the light source any objects with definite shapes, we see the development of the “photogenic” drawing. Leaving out the chemical formulations and reactions, for which there is ample treatment on websites and books, just worth to remember that the compounds used by Herschel to create the original solution were ammonium iron citrate and potassium ferricyanide. The solution was prepared and used at the time as it quickly became unstable and no longer usable, while the support was mainly fibrous paper, very suitable to retain the blue color of Prussia (ferric ferrocyanide) that is formed thru light’s action. Once exposed to the sun (or rather, to ultraviolet rays) and formed the image, it is sufficient to wash the print in running water in order to fix the blue part and remove all the remaining iron in excess: an extremely simple procedure and whose result can be checked live to get the best possible outcome.
Immediately in the first years of the discovery, the new process was extensively experimented and admirable is in particular what made by Anna Atkins who already in 1843 published the book “British Algae: Cyanotype Impressions”, a kind of herbarium created by putting various plant specimens to paper sensitized with the Herschel solution.
Over the years the Cyanotype has found extensive application also for the ability to apply the sensitive solution to a large number of media, such as fabric, wood, glass in addition to paper; being in itself a very flexible procedure, several modifications to the composition were proposed, especially in terms of the ratio and concentration of the two solutions; one of the most important changes was introduced by Mike Ware and consists in replacing the ammonium iron citrate with the ammonium iron oxalate, a variation that allows you to have a solution much more stable and usable even after several days. This is the basis of the various kits that can be found on the market today (and of which we will publish in a few days a review) and is the one that guarantees the best and repeatable results.
In recent years, then, Cyanotype is experiencing a new period of interest thanks to the possibility of using transparent inkjet print sheets and, therefore, printing all kinds of images, such as those coming from digital cameras:
This has allowed a new creative ferment that makes it the oldest technique perhaps most used in absolute; and the results that you get are right from the start, as soon as you learn to control the exposure process, valid and fulfilling. There is no shortage of space for technical experimentation, both for the choice of the supports and for the concentrations and relationships between the solutions, which all have an effect on the final quality of the image, up to the washing process that can be modified to get variation in the tone of the image.
Web is full with a variety of information that can satisfy every curiosity, which is not the purpose of this brief historical note. As a reference resource we refer to this address https://blog.scienceandmediamuseum.org.uk/introduction-cyanotype-process/from where, in addition to the technical information, you can access a first bibliography to further study.